The overall objectives of the proposed works are: 1) to clearly delineate the molecular characteristics of Fc gamma receptor-phospholipase A2 present on the surface of human lymphocytes; 2) to localize two parts within an Fc gamma R molecule that display Fc- and phosphatidylcholine (PC)-binding activity, respectively; 3) to examine the properties of membrane-bound, affinity purified phospholipase A2 of human T cells (peripheral blood T cells and cultured human T cell lines (such as Molt 4F)) in comparison with Fc gamma R-phospholipase A2 isolated from human B cells (chronic lymphocytic leukemia cells and cultured human B cell lines); and 4) to examine the potential roles of phospholipase A2 on the surface of B and T cells in the regulation of the immune response. The isolation of Fc gamma R proteins follows the previously reported five step procedure (sequential affinity chromatography on heat-aggregated IgG- and Fc-fragment-Sepharose, gel filtration, and isoelectric focusing). Plasma membrane-associated phospholipase A2 will be isolated by affinity chromatography on rac-1-(9-Carboxy)nonyl-2-hexadecyglycero-3-phosphorylcholine-Sepharose AH. Characterization of the isolated molecules and localization of Fc- and PC binding sites will follow the standard protein chemistry technique. Roles of Fc gamma R-phospholipase A2 in the immune regulation will be examined by measuring the levels of various substances that are involved in prostaglandin synthesis.